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POCreating a Sudoku in Java
 

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    <p>I'm creating a program that invents a new Sudoku puzzle. The way I initially planned on doing this is by inventing a new puzzle and then removing random numbers. However, the algorithm I use (seen below) to create a new puzzle can take up to 5 minutes to make one. Does anyone have any faster solutions?</p> <h2>Creation Algorithm</h2> <hr> <pre><code> for (int x = 0; x &lt; boardWidth; x++) //boardWidth is the number of fillable squares wide and high the board is. (9 for a standard Sudoku board) { for (int y = 0; y &lt; boardWidth; y++) { int errorCount = 0; do { boardVals[y][x] = (byte)(rand.nextInt(boardWidth) + 1); errorCount++; if (errorCount &gt; Math.pow(boardWidth, 4)) //If the square has been tried to be filled up to boardWidth^4 times (6,561 for a standard Sudoku board), it clears the board and starts again. { resetBoard(); x = 0; y = 0; break; } }while (!boardIsOK()); //boardIsOK() is a method that checks to see if the board is solvable, ignoring unfilled squares. } } </code></pre> <h2>Methods:</h2> <hr> <pre><code> private boolean boardIsOK() { for (int i=0; i &lt; boardWidth; i++) { if (!setIsOK(getRow(i))) { return false; } if (!setIsOK(getCol(i))) { return false; } } for (int x=0; x &lt; boardSegs; x++) { for (int y=0; y &lt; boardSegs; y++) { if (!areaIsOK(getSquare(x,y))) { return false; } } } return true; } private byte[] getRow(int index) { return boardVals[index]; } private byte[] getCol(int index) { byte[] b = new byte[boardWidth]; for (int i=0; i &lt; boardWidth; i++) b[i] = boardVals[i][index]; return b; } private byte[][] getSquare(int xIndex, int yIndex) { byte w = (byte)(boardWidth / boardSegs), b[][] = new byte[w][w]; for (int x=0; x &lt; b.length; x++) { for (int y=0; y &lt; b[x].length; y++) { b[y][x] = boardVals[y + (yIndex * w)][x + (xIndex * w)]; } } return b; } private boolean setIsOK(byte[] set) { for (int i=0; i &lt; set.length - 1; i++) { for (int j=i + 1; j &lt; set.length; j++) { if (set[i] == set[j] &amp;&amp; set[i] != NULL_VAL &amp;&amp; set[j] != NULL_VAL) { return false; } } } return true; } private boolean areaIsOK(byte[][] area) { int size = 0; for (int i=0; i &lt; area.length; i++) { size += area[i].length; } byte[] b = new byte[size]; for (int x=0, i=0; x &lt; area.length; x++) { for (int y=0; y &lt; area[x].length; y++, i++) { b[i] = area[x][y]; } } return setIsOK(b); } </code></pre> <p>resetBoard() simply fills the board with NULL_VAL.</p>
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    1. CODescribe the constraints to the problem in Prolog and run that program using [TuProlog](http://alice.unibo.it/xwiki/bin/view/Tuprolog/), a library for embedding Prolog in Java environments.
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    2. COdunno what that is or how it will help.
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